Fix @node pointer errors

Unfortunately, you cannot reliably use periods, commas, or colons within
a node name; these can confuse the Info reader.

After creating Info files with `makeinfo ledger3.text`, installing them and viewing them with the Info reader, you cannot navigate past "Total-commodity-prices". The Info reader complains that the "Prices vs" node does not exist. The Info reader subsequently becomes stuck in this subsection.